U.S.-backed Syrian Democratic Forces have defeated Islamic State fighters in the city of Tabqa and have seized Tabqa Dam, a key objective for the militias before a planned attack on the terror group’s de-facto capital, Raqqa.

The SDF, a multi-ethnic group which includes Kurdish fighters and Syrian Arab Coalition (SAC) fighters, had been battling Islamic State for weeks in Tabqa, about 40 kilometers west of Raqqa, with the help of coalition airstrikes and U.S. special forces advisers.

Syrian Democratic Forces (SDF) fighters pose with foreign volunteer fighters inside Tabqa military airport after taking control of it from Islamic State fighters, west of Raqqa city, Syria April 9, 2017.

"This is yet another victory by the SAC and the SDF, our most committed and capable ground force partners in the fight against ISIS,” coalition spokesman U.S. Col. John Dorrian said in a Central Command statement released Thursday.

U.S. Central Command, which oversees U.S. military operations in the Middle East, said approximately 70 Islamic State fighters had conceded to the SDF's terms, which included dismantling bombs surrounding the dam, surrendering their heavy weapons and withdrawing all remaining fighters from Tabqa.

The SDF accepted the IS surrender in order “to protect innocent civilians" and to preserve the Tabqa Dam infrastructure, which hundreds of thousands of Syrians rely on for water, agriculture, and electricity, Central Command said.

Map of Tabqa Dam.

After Wednesday’s SDF victory, the coalition said it tracked fleeing Islamic State fighters and targeted those who could be hit without harming civilians.

The coalition said Thursday that Islamic State had moved its external attack planning operations to Tabqa after their defeat in Manbij in order to avoid coalition airstrikes in Raqqa.

“The operation to seize the Tabqa Dam, airfield and city disrupts ISIS operations in Raqqa and their ability to defend the city and plan and execute external attacks against the West,” the coalition said.

U.S. airmen had airlifted SDF forces behind IS lines to launch the attack that captured the Tabqa airfield in late March, U.S. General Carlton Everhart, commander of the Air Force's Air Mobility Command, told VOA after the March assault.

FILE - A Syrian Democratic Forces (SDF) fighter walks near destroyed airplane parts inside Tabqa military airport after taking control of it from Islamic State fighters, west of Raqqa city, Syria April 9, 2017.

American engineers and crews were repairing and restoring the airfield while the SDF continued its fight for Tabqa city and Tabqa dam.

The seizure of Tabqa and Tabqa Dam comes just days after President Donald Trump authorized the Pentagon to equip the Kurdish elements of the Syrian Democratic Forces.

Chief Pentagon Spokesperson Dana W. White said Tuesday the Kurdish component, which makes up more than half of the SDF fighters, would be armed "as necessary to ensure a clear victory" over Islamic State in Raqqa, Syria.

FILE - This April 30, 2017, photo provided by the Syria Democratic Forces (SDF), shows a fighter from the SDF carrying weapons as he looks toward the northern town of Tabqa, Syria.

A military official told VOA the United States will provide Kurdish forces around Raqqa with small arms, machine-guns, ammunition, and armored vehicles to counter improvised explosive devices and construction equipment.

“Weapons will be meted out to achieve limited military objectives,” the military official said Tuesday.

Ankara opposes Washington's alliance with Syrian Kurdish forces fighting Islamic State. Turkey contends the SDF's Syrian Kurdish militia, known as the YPG, is a terrorist group affiliated with the outlawed PKK, the Kurdistan Workers' Party, a terror group that has been battling the Turkish state for many years.